i) Field of the Invention
The present invention relates to a manufacturing method and apparatus of a phase shift mask blank which is suitable particularly for ArF or F2 excimer laser.
ii) Description of the Related Art
In recent years, it has become clear that high resolution and depth of focus are two important properties required for photolithography but are in a contradictory relation with each other, and that a practical resolution cannot be enhanced using only a short wavelength laser and an exposure apparatus with a lens having a high numerical aperture (“NA”). (Monthly Semiconductor World 1990.12, Applied Physics Vol. 60, November, 1991, and the like).
In such a situation, phase shift lithography has been noted as the next-generation photolithography technique, and partially brought to practical use. Phase shift lithography is a method for enhancing the resolution of photolithography by changing only a mask without changing an optical system. When a phase difference is applied between exposure lights transmitted through the photo mask, mutual interference of the transmitted lights can be utilized to rapidly enhance the resolution.
The phase shift mask is a mask which uses light strength information together with phase information. Various types of masks are known such as Levenson type, auxiliary pattern type, and self-matching type (edge emphasizing type). These phase shift masks have a complicated structure and require a high degree of manufacturing technique as compared with the conventional photo mask which uses only light strength information.
In recent years, a so-called halftone type phase shift mask has been developed as one of the phase shift masks.
In a halftone phase shift mask, a light semi-transmission section has two functions: a shield function of substantially shielding the exposure light and a phase shift function of shifting (usually reversing) a light phase. Therefore, it is unnecessary to separately form a shield film pattern and a phase shift film pattern. This type of phase shift mask is structurally simple and easy to manufacture.
In a halftone phase shift mask, a mask pattern is processed by a dry etching process. However, when providing the shield function and phase shift function by separate layers, a high degree of control is necessary for both the layer having the shield function and the layer having the phase shift function in order to obtain a satisfactory pattern shape. On the other hand, when creating a single-layer light semi-transmission portion having both the shield function and the phase shift function, a single etching process can be used. Therefore, the manufacturing process of such a mask can be simplified, and a satisfactory pattern shape can easily be obtained.
For the halftone phase shift mask, as shown in FIG. 10, a mask pattern formed on a transparent substrate 100 is constituted of a light transmission portion (transparent substrate exposed portion) 200 for transmitting a light which is strong enough to substantially contribute to exposure and a light semi-transmission portion (shield and phase shifter portion) 300 for transmitting a light which is not strong enough to substantially contribute to the exposure (FIG. 10A). Additionally, the phase of the light transmitted through the light semi-transmission portion is shifted to a substantially reversed relation with respect to the phase of the light transmitted through the light transmission portion (FIG. 10B). The oppositely-phased lights transmitted in the vicinity of a boundary between the light semi-transmission portion and the light transmission portion cancel each other on account of diffraction phenomenon. Thereby, light strength in the boundary is substantially set to zero and, in contrast, resolution in the vicinity of the boundary is enhanced (FIG. 10C).
Additionally, the light semi-transmission portion or film (phase shift layer) in the halftone phase shift mask or blank needs to indicate a required optimum value with respect to both transmittance and phase shift amount. For example, (1) the transmittance in exposure wavelength of i-ray, KrF excimer laser, ArF excimer laser, or the like can be adjusted in a range of 3 to 20%, (2) a phase angle can be adjusted usually to a value in the vicinity of 180° in the exposure wavelength, and (3) the transmittance needs to be usually testable in a range of 65% or less in test wavelengths such as 257 nm, 266 nm, 364 nm, and 488 nm.
However, by shortening the wavelength of the laser for use in the exposure to ArF excimer laser (193 nm) from i-ray (365 nm) and KrF excimer laser (248 nm), the following problem is generated in the conventional halftone phase shift mask and the manufacturing method of the mask.
That is, in mass production of the phase shift mask blanks, when there are dispersions of the phase angle and transmittance among the blanks or in the plane, the yield is bad. Particularly in mask blanks for the short wavelength of ArF or F2 excimer lasers, the dispersions of the phase angle and transmittance among the blanks and in the plane in conventional mask blanks for i-ray and KrF excimer laser are large, and the yield is bad. Therefore, the resulting mask blanks cannot be used.